1. Field of the Invention
This invention relates to a method for processing metal cord and more particularly to a method for processing cord containing welds continuously through a mechanical straightener without breakage.
2. DESCRIPTION OF THE PRIOR ART
In order for various industrial processes to be economical they must be essentially continuous in nature. That is, the number of steps must be minimal to maintain a high rate of production coupled with a minimum amount of handling or stoppages in the production cycle.
One such industrial process is the treatment of steel cord for reinforcing rubber composites, such as hoses, conveyor belts and pneumatic tires. In processing steel cord a number of filaments are twisted together to form a cord or strand on a strander, double twist buncher or ring twister. After the strand or cord is formed, certain other steps must be performed to produce a usable product. For example, the twisted product must be cleaned and then coated with an adhesive material to insure adhesion within the rubber composite. Each time the product is treated, it is generally unwound and then rewound. It is readily apparent that for this process, consisting of numerous steps, to be economical it must be continuous. That is, to minimize handling and interruptions each package or spool of cord must be fastened in some way to the preceding package or spool. The spools can be knotted together, but the generally accepted manner is by welding the head end of one spool to the tail end of another spool.
Welding, however, presents certain problems. The consumers of adhesive coated steel cord or strand have established stringent quality requirements. One very important requirement is straightness. That is, when the product is unwound from its package it must lie straight without any twist or curliness. For instance, a twenty foot (6.08meter) length of cord must not deviate more than three inches (7.62 cm) from a straight line. Assembling cords and strands from filaments induces stresses that cause the product to take helical configuration. The tendency to take this shape can be eliminated and a straight cord can be obtained by passing it through a mechanical straightener or heat treating as disclosed in copending U.S. Pat. Application Ser. No. 229,515, filed on Feb. 25, 1972 and assigned to the assignee of this invention.
To insure a continuous feeding of cord on succeeding spools must be fastened one-to-another. As the supply of cord on one spool is exhausted cord must immediately start feeding from another spool. It has been found that welding the cords together is the best approach to attain continuous feeding. A proper weld does not appreciably change the cross-section of the cord as other techniques such as tying the ends together and is sufficiently strong to hold the two cord sections together during processing. Welding can be performed before or after the cord or strand has been straightened. Regardless of when the product is welded, that is, before or after straightening each approach presents certain problems.
If the cord is welded after straightening an accumulator capable of accumulating a sufficient amount of cord to insure continuity of processing is required. For example, if the cord is traveling at a line speed of 450- 500 fpm (135- 150 mpm) and it takes two minutes to complete welding and post weld heat treating an accumulator is needed capable of storing 900 to 1,000 feet (274- 305 meters) of cord. Employing or installing an accumulator increases operational and maintenance costs as well as capital expenses.
Welding prior to straightening is another alternative. The cord package contains a head segment and tail segment, two portions of the cord length easily identified from the remainder of the package. The tail segment of a first spool can be welded to the head segment of a second spool and then continuously passed to a straightener. This insures a continuous process without the use of an accumulator. It has been found that continuously passing cord containing welds through a mechanical straightener is not commercially reliable. The weld must be metallurgically sound, ductile enough to withstand bending stresses in the mechanical straightener yet strong enough to join the spool ends together. To consistently produce welds of this nature is extremely difficult on a production basis. For a reliable operation with a minimum amount of down time nearly 100 percent weld performance or no weld breaks is required. This performance has not yet been attained by passing welds through a mechanical straightener.
This invention provides for a continuous operation wherein weld breakage is not incurred. The resultant product is straight and the use of an accumulator is not required.